I also have had useful life out of otherwise defunct nicads. (e.g 2-3
years extra on a Makita battery drill).

Also I have recovered some gel lead-acid batteries to a useful amount
by adding water. The success of this seems to be dependent on the
failure mode of the battery however. It works with some, but not
others. (I think the ones that worked best had just dried out by
being on a constant voltage trickle charger set slightly too high). It
took about a week before the water soaked through enough to get useful
storage capacity back IIRC

Also highly sulphated flooded batteries have been recovered by
applying a much higher recharge voltage than normal and reducing this
as the charge current rises. A few cycles of this (charge - discharge)
and they have usable storage capacity again, although it is reduced,
and the internal resistance is higher.

> Cedric Chang wrote:
>> For those of you who have restored dead NiCads or Lead Acid
>> batteries, was it worth it ?
>>
>> For myself, it was not worth it other than to say I could do it. The
>> restored batteries never lasted long enough to be worth the trouble.
>> cc
> Definitely worth it on nicads. I used to do miles of wire-wrapping with
> an electric eraser tool and wire bit from Vector. The nicads were old
> and would develop shorting crystals (or whatever it is that shorts them)
> and they would not charge. Zapping them with a big cap allowed me to
> continue to use them well over 5 years after they began to go bad.
>
> Finally put the whole enchilada behind me with Alberta Printed Circuits.
> Plus I still have not figured out how to do wire wrapping with SMD
> parts...

> For those of you who have restored dead NiCads or Lead Acid
> batteries, was it worth it ?
>

For NiCD/NiMH:
1. It depends on the failure mode as others have stated. Most packs are
worthwhile because they are due to unbalancing of the cells that are
connected in series. I have a simple current charger that I use to trigger
charge at C/10 or less (LM317 with replaceable resistor) without opening the
case. More serious case shall need opening up the case to recondition
individual cell. Quite a hassle.

2. For my case, shorted cell in a series pack is not so worthwhile. Mainly
because of the hassle of dealing with the enclosure. But if they are normal
AA/AAA/etc cell, recovering them should be worthwhile, but then you can't
have your longlife(eneloop) NiMH battery for a while :-)

>
> For me, it essentially turns out that NiCd, NiMH, and LA batteries
> are not "worth it", period. They can't stay in a charger getting
> "topped off", they don't store charged, and storing them uncharged
> seems to quickly lead to a condition where they will no longer take a
> charge. I'm prepared to believe that there are circumstance where
> they behave better than that (use every day, charge overnight), but
> my usage patterns don't seem to match... I don't care whether the
> problem are "memory", or "over charging" or something else entirely.
> They just don't work for me in most applications.

To be fair, yours is more of a "fitting" problem, nothing wrong with the
"pants" :-)

The price for eneloop and alike is about S$5 per cell. At this price, it is
not easy to phase most alkaline cell usages. But the R2U cell with their
discount comes to about S$2.00 or less, making it a worthwhile replacement
for more alkaline replacement. I have not tried them, seeking for reviews.
The Sanyo and GP low discharge cells are working very well here in digital
camera, power screwdriver, emergency charger for mobile. I also use them in
a portable power supply with the AnyVolt Universal DC converter. <http://www.dimensionengineering.com/AnyVolt.htm>

In my experience, this does not apply so much to Lead Acid batteries.
To me, LA are the most forgiving type out there. It is easy to damage
Lithium Ion (and apparently they do not like to be continually charged
or even stored fully charged, either). LA self discharge is pretty
slow. Takes about 6 months to drain to about 50 to 70% of start (that
is, 50 to 70% remaining).

>
>>> For those of you who have restored dead NiCads or Lead Acid
>>> batteries, was it worth it ?
>
> For me, it essentially turns out that NiCd, NiMH, and LA batteries
> are not "worth it", period. They can't stay in a charger getting
> "topped off", they don't store charged, and storing them uncharged
> seems to quickly lead to a condition where they will no longer take a
> charge. I'm prepared to believe that there are circumstance where
> they behave better than that (use every day, charge overnight), but
> my usage patterns don't seem to match... I don't care whether the
> problem are "memory", or "over charging" or something else entirely.
> They just don't work for me in most applications.
>
> Since this means that I tend to get something like 5 to 10 uses out
> of a NiCD pack before they need "attention", if a zapping gets
> another 5 or 10 charges, that's pretty good...
>
> Li-ion are WONDERFUL in comparison. I want Li in everything!
> I'm still trying out the "low self discharge" NiMH ("eneloop" and
> similar); looks like they might be OK.
>
> BillW
>

Memory in NiCds is long debated and minimal with proper
treatment. Memory in NimH does exist (the manufacturers say)
but is small and easily removed when a deep cycle is
resumed. Cause is crystal structure effects and % reduction
is small at worst in NimH.

Prius uses NimH and gets about 10 year life by aggressive
battery management.

Modern consumer NimH of large energy density (say over 1600
mAh in an AA size) mostly do not support long term trickle
charge. Lower capacity cells do. NiCd do. Thermal issues may
be the cause.

Limiting the top and bottom end storage (10% each end) of
NimH is said to allow 2000 cycles of use. (See eg OLTPC). As
little as 500 cycles in more normal use (see manufacturers'
data sheets).

LiIon have typically longest life if stored at about 2/3
capacity. As this is about at the transition from constant
current to constant voltage charge it is easy to do.

Typical LiIon have a 4.3V max charge voltage. Reducing this
to 4.2V markedly increases cycle life at the cost of
reducing charged capacity somewhat. Seems like an excellent
tradeoff to me.

Many people claim desulphation and pulse charging restore
dead as dead LA to life. I can't comment usefully but years
ago experience with desulphation was not good.

LA have excellent shelf life. Energy density is low but
charged and discharged half intelligently they work very
well. I see them as an excellent choice where size and
weight are not issues and disposal can be controlled.

If NiCd packs go flaky after 10 cycles I'd suspect either
low quality cells or low quality chargers. Chargers in cheap
power tools are often very poor - often a series resistor
from a power supply. Boiled NiCds have low lives. My
experience of de-whiskering NiCds is that it often works but
a cell thus treated tends to do it again easily. Connection
of a reverse Schottky diode across each NiCd will stop
whiskering!!!

Vaguely related: FWIW, connection of a FORWARD SILICON
diode across silicon solar cells makes them much much more
immune to partial shadowing effects. A solar panel with a
single shadowed cell will have its output current reduced to
about the capability of the shadowed cell,

> In my experience, this does not apply so much to Lead Acid
> batteries.
> To me, LA are the most forgiving type out there. It is
> easy to damage
> Lithium Ion (and apparently they do not like to be
> continually charged
> or even stored fully charged, either). LA self discharge
> is pretty
> slow. Takes about 6 months to drain to about 50 to 70% of
> start (that
> is, 50 to 70% remaining).

>>>> For those of you who have restored dead NiCads or Lead
>>>> Acid
>>>> batteries, was it worth it ?

>> For me, it essentially turns out that NiCd, NiMH, and LA
>> batteries
>> are not "worth it", period. They can't stay in a charger
>> getting
>> "topped off", they don't store charged, and storing them
>> uncharged
>> seems to quickly lead to a condition where they will no
>> longer take a
>> charge. I'm prepared to believe that there are
>> circumstance where
>> they behave better than that (use every day, charge
>> overnight), but
>> my usage patterns don't seem to match... I don't care
>> whether the
>> problem are "memory", or "over charging" or something
>> else entirely.
>> They just don't work for me in most applications.
>>
>> Since this means that I tend to get something like 5 to
>> 10 uses out
>> of a NiCD pack before they need "attention", if a zapping
>> gets
>> another 5 or 10 charges, that's pretty good...

>> Connection of a reverse Schottky diode across each NiCd
>> will stop
>> whiskering!!!

> How does that work ? Prevents reverse polarity in the cell
> ?

Yes.
The Schottky voltage is below the voltage required to form a
plated whisker.
A nice trick.

The Silicon solar cell forward diode is also "nice". A
shadowed cell has its CURRENT capability much reduced.
When the voltage from the other cells is applied to the
shadowed cell the diode conducts and it is effectively
bypassed with a diode drop of voltage loss plus the loss of
the voltage from the shadowed cell. Without this a fleeting
shadow or as little as a waving branch or a leaf shadow can
effectively shut down a whole panel while the shadow
remains.